The development of normal skin depends upon the elaborate interaction of numerous cell types derived from ectoderm, neuroectoderm and mesoderm. Nevi and other hamartomas presumably develop when aberrant cellular interactions lead to deposition of cells in inappropriate locations. Factors important for communication between keratinocytes, melanocytes, fibroblasts and other cell types likely orchestrate proper cell positioning and their reactivation in the adult may lead to cancer and metastasis. Determining molecules responsible for induction of benign hamartomas, like blue nevi, is a first step in elucidating the mechanisms of tumor formation and progression. Here we will use a skin reconstitution model in an immunodeficient mouse grafting system to begin to decipher the inductive and inhibitory signals that lead to the formation of a blue nevus. In 1996, Prouty and coworkers found that when they combined specific types of fibroblast cell lines with neonatal epidermal cells and grafted the mixture onto immunodeficient mice, the grafted area developed a common blue nevus (CBN) or a nevus sebaceus of Jadassohn (NSJ) depending on which cells were used. Grafting of epidermal cells alone resulted only in a scar, while combining epidermal cells with fresh whole dermis regenerated normal appearing skin possessing hair follicles, melanocytes and sebaceous glands. In this study we will use gene expression microarrays to compare mesenchymal cell lines that induce blue nevi with those that do not. We plan to identify candidate genes important for the migration, survival and localization of melanocytes. These candidate genes will be stably overexpressed in non-inductive fibroblast cells to test for induction of a blue nevus phenotype. Ultimately, we will evaluate whether blue nevi and other melanocytic hamartomas from humans express the identified genes. The results from these studies will form the foundation for a K-award or new investigator RO1 for Dr. Castelo-Soccio, the principal investigator.